MAZRAQ, YEMEN -- From his tent made of blankets, Ali al-Majeshri stared at the tarpaulin tents in the refugee camp across the road. Five days before, he and his family had arrived at this wretched patch in a failing nation, driven here by a civil war that overnight had become a regional conflict. Bombs, bullets, threats -- this was what they were escaping. So were 15,000 other Yemenis.

And so the Majeshris waited to enter an overcrowded camp with better tents, and for someone to care. "We haven't received anything," muttered Majeshri, 55, sipping hot tea as flies buzzed around his face.

A humanitarian crisis in Yemen, the poorest country in the Middle East, has worsened in recent weeks as the civil war between the government and Shiite rebels spilled across the border into Saudi Arabia. The turmoil is adding to the stress on a country already beset by multiple emergencies, including calls for secession in the south and a growing al-Qaeda threat.

The crisis, coupled with high unemployment and a lack of government services, is also putting additional pressure on overburdened tribal communities. Western diplomats and Yemeni analysts say the strain could create new legions of poor and vulnerable people who would be easy recruits for al-Qaeda and other extremist groups.

A quarter of the 700,000 Yemenis in the country's northernmost province have been displaced by the five-year-old war. Recently, more than 900 people have been arriving at the Mazraq camp every day, U.N. officials say. Nearly 700 children in the camp are suffering from severe malnutrition, a chronic problem in Yemen. At least six children have died in the past month, according to UNICEF officials.

In recent days, 240 villages and 50 schools in Saudi Arabia have been evacuated, and many Saudis have been forced to flee across the border to Mazraq.

"The overall development gains we've made have been swamped by the conflict," said Naseem-Ur-Rehman, UNICEF's chief spokesman in Yemen. "It could take 10 years or more to catch up to the pace to which we had pushed through."

The rebels, called Hawthis after the name of their leader's clan, launched their rebellion in 2004, seeking greater religious and political representation. They adhere to the Zaydi brand of Shiite Islam. The Zaydis constitute a minority community in this mostly Sunni country.

In August, the government launched an all-out military campaign in Yemen's northern Saada province, where the Zaydis are a majority. Two weeks ago, Saudi Arabia bombed sites in Yemen after the rebels staged a cross-border attack that killed a Saudi border guard. The rebels accuse Saudi Arabia of backing Yemen's government.

The entry of Saudi Arabia, which considers itself the guardian of Sunni Islam, has raised fears of a proxy war in the region between the kingdom and its arch rival, Shiite Iran. Yemen and Saudi Arabia accuse Iran of backing the Hawthis in an effort to gain influence in the region, an allegation that the rebels and Tehran deny.

On Tuesday, Maj. Gen. Hassan Firouzabadi, chief of staff of Iran's armed forces, accused Saudi Arabia of killing Yemeni Shiites, declaring "the onset of Wahhabi state terrorism, which is very dangerous for Islam and the region," according to Iran's state-run Islamic Republic News Agency. Wahhabism is a fundamentalist form of Islam practiced in Saudi Arabia.

Firouzabadi added that the conflict could spread and "engulf all Muslims everywhere."

Meanwhile, Saudi clerics and newspapers have accused the rebels of colluding with Iran to spread Shiite Islam into the nexus of Sunni Islam.

Mazraq, the largest of several camps in the province, has doubled in size in the past month. Most of the arrivals are women and children, clutching only what they could carry. Their refuge is less than five miles from the front lines. "We can hear the bombs," said Khalid al-Shaibani, UNICEF's coordinator for the camp.

Eight to 10 families share each tent, said aid workers, who are providing drinking water, food, bedding and other essential supplies to the displaced. But the vast majority of the displaced are still trapped in war-torn areas, inaccessible to aid agencies. Many victims struggle to reach medical and health facilities. In the provincial capital of Saada and nearby areas, there is only one functional hospital, according to the International Committee of the Red Cross.

At Mazraq, nearly everyone has a tale of violence and abuse. Misr Ali Ahmed al-Walabi, 45, and 30 of his relatives fled into Saudi Arabia three months ago. Two weeks ago, after the rebel attack, they fled deeper into Saudi Arabia, as bombs and bullets rained around them, Ahmed said. But Saudi soldiers accused them of spying for the Hawthis and threw them in jail. The next day, they were driven to the Yemeni border and deported.

"We were happy to return to our homeland," said Ahmed's brother, Muhammed, as they sat inside their tent, where all 30 relatives live. "But now we are suffering again."